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Purpose We experienced 10 cases of ossification of the ligamentum flavum OLF and report the neuroradiologic and pathologic findings. The pathogenesis of OLF is discussed, and a literature review is provided. Materials and Methods We treated 10 cases of thoracic OLF between 2010 and 2016. Neurologic symptoms and the Japanese Orthopaedic Association JOA score were evaluated. The postoperative recovery rate and JOA score RR% were calculated and compared with the preoperative results. Computed tomography CT and magnetic resonance imaging MRI were performed, and all 10 cases underwent laminectomy. Pathologic findings were evaluated. Results The age range of patients was 34 82 years, with 8 male and 2 female patients. All 10 cases developed myelopathy at the thoracic cord level. CT showed beak like ossification extending to the intervertebral foramen. Pathologic findings demonstrated laminar ossification in the ligamentum flavum. Preoperative JOA scores ranged from 3 to 19 mean 9.3 5.1. One year postoperative JOA scores ranged from 17 to 29 mean 23.4 4.7 , and the RR% increased from 53.8 to 100 mean: 71.3 11.5. Pathologic findings demonstrated laminar deposition of calcium phosphate in the intervertebral foramen. Chondrocytes enclosed by calcification and laminar hyaline cartilage were observed. Osteoblasts were observed in deposits of calcium phosphate. Conclusions OLF is independent of spondylotic change and calcification of spinal ligaments. The neuroradiologic and pathologic findings suggested that chronic mechanical stimulation compression and tension of the ligament leads to gene expression and induction of transforming growth factors e.g., bone morphogenetic growth factors, etc. , resulting in chondral ossification. Laminectomy for appropriate levels was effective.